WHO: Teachers or School Administrators looking to create online pages for sign-ups.
HOW: Create an account at SignUp Genius, Click on create sign-up, and follow the instructions.
WHEN: I have used this in the past for creating sign-up sheets for Parent-Teacher Conferences. It has been very successful, and I have heard from the parents that it was easy for them to use. There does seem to be a limit to the system for the amount of slots that can be made available. Typically I have to either split up the days, or split up the teachers, in order to get every slot available for sign-up.